1. Field of the Invention
The present invention relates to a hard disk drive (HDD). More particularly, the present invention relates to a head stack assembly (HSA) of an HDD.
2. Description of the Related Art
A hard disk drive (HDD) is a device used in personal computers (PCs), MP3 players, mobile phones, and the like to store and retrieve data. To this end, an HDD includes a data storage disk, a spindle motor for rotating the disk, and a magnetic head that reads and writes data from and onto the disk. The head is embedded in a head slider, and when the HDD is operating, the head slider floats a predetermined distance above the disk while the disk is rotated by the spindle motor. The head slider is part of a head stack assembly (HSA) which is controlled to move the magnetic head over specified tracks of the disk. The tracks extend along concentric circles, respectively, whose centers coincide with the center of the disk.
The HSA also includes a swing arm that moves the head slider to a location over a specified track of the disk, and a suspension to which the head slider is mounted. The suspension supports the head slider during a read/write operation and maintains the spacing between the head slider and the recording surface of the disk. However, the magnetic head may deviate laterally from a specified track due to vibrations in the disk or the HSA. Such vibrations may be created when the HDD is disturbed or when the spindle motor of the HSA is running. This malfunction is referred to as the magnetic head being “off-track”. FIG. 1 is a conceptual diagram illustrating an off-track state which may arise when the disk of the HDD is vibrating, and FIG. 2 is a conceptual diagram illustrating an off-track state which may arise when the suspension bends due to vibrations.
Referring to FIG. 1, a magnetic head h0 of a head slider 27 and a specific track T of a disk 10 are located at vertically aligned positions h0(d0), T(d0), respectively, when a read/write operation begins. Therefore, at this time, the magnitude of the off-track state of the magnetic head h0 is 0. However, the outer circumference of the disk 10 and the head slider 27 of the HSA vibrate up and down, as illustrated by dotted lines, when the HDD vibrates at a specific frequency. As a result, the magnetic head h0 becomes misaligned with the track T of the disk 10, i.e., the magnetic head h0 runs ‘off-track due to disk vibration’. More specifically, the track T is displaced radially outwardly from position T(d0) to position T(d1) when the disk 10 moves downwards while vibrating. As a result, the suspension undergoes torsion and thereby displaces the magnetic head h0 radially inwardly from position h0(d0) to position h0(d1). On the other hand, the track T is displaced radially inwardly from position T(d0) to position T(d2) when the disk 10 move upwards while vibrating. In this case, the twisting of the suspension displaces the magnetic head h0 radially outwardly from position h0(d0) to position h0(d2). Therefore, the magnetic head h0 runs off-track when the head slider 27 moves upwardly or downwardly along with the vertical movement of the outer circumferential portion of the disk 10.
U.S. Pat. Nos. 6,920,018 and 6,958,879 disclose HSAs aimed at reducing the amount by which the magnetic head runs off-track due to disk vibration. To this end, the HSA has a suspension and a connection plate attached at a specific bias angle, or a plurality of members of different thicknesses connecting the suspension and the connection plate. An HSA according to this prior art can reduce the amount by which the magnetic head would otherwise run off-track due to disk vibration because the HSA moves the head slider radially outwardly when the head slider moves downwards and the suspension undergoes torsion, and moves the head slider radially inwardly when the head slider moves upwards and the suspension undergoes torsion.
However, the HSAs disclosed in the prior art can not suppress the tendency of the magnetic head to run off-track when vibrations transmitted to the suspension cause the suspension to bend up and down. That is, referring to FIG. 2, a suspension 25 of the HSA may vibrate up and down irrespective of the disk. In this case, the head slider 27 connected to the suspension 25 also vibrates up and down, resulting in the magnetic head running ‘off-track due to suspension bending’. More specifically, the bending of the suspension 25 as it vibrates causes the suspension to become alternately convex and concave. The magnetic head of the head slider 27 is displaced towards the center of the disk 10 (from position h0(s0) to position h0(s1)) when the suspension 25 becomes convex. As a result, the magnetic head runs on one side of the desired track T. On the other hand, the magnetic head of the head slider 27 is displaced towards the outer circumference of the disk 10 (from position h0(s0) to position h0(s2)) when the suspension 25 becomes concave. As a result, the magnetic head also runs on the other side of the desired track T.